Scheduling Seasonal Canine Heartworm Examinations

Canine heartworm disease is a serious mosquito-spread infection. The American Heartworm Society estimated 250,000 dogs are affected each year in the United States by canine heartworm. The disease, caused by the parasite Dirofilaria immitis, is found worldwide.

Life Cycle

Heartworm disease is spread by mosquitoes feeding on the blood of an infected animal and then feeding on a non-infected animal. The adult heartworms live in the right ventricle of the heart and in the lung arteries. They can grow to 9 to 16 inches long and live for three to five years. The adults mate and spread tiny heartworms (microfilaria) into the bloodstream. The microfilaria live in the bloodstream for one to three years or until they are ingested by a mosquito. In the mosquito they develop into larva in 8 to 28 days. This infected mosquito then bites a dog depositing the larva on the skin. The larva enter the bitten dog's bloodstream through the wound left by the mosquito.

In the newly infected dog, the larva reaches the lung arteries around 100 days after the bite. Here they develop into adults which migrate to the heart's right ventricle. Six to seven months after the infected mosquito bites the dog, microfilaria are produced by the adult heartworms.

Dogs most at risk for heartworm disease include unprotected dogs in areas where heartworm is established, and dogs which spend a lot of time outdoors. The average age of affected animals is three to eight years of age.

Symptoms of Heartworm

Most infected dogs either don't show symptoms of being infected or they will show very mild symptoms, such as coughing. Advanced disease leads to severe symptoms. These include inability to tolerate physical activity, extreme weight loss and fluid build up in the abdomen. These severe symptoms indicate heart failure and the dog may not be able to be successfully treated when this occurs.

Preventing Heartworm

Scheduling a yearly heartworm test is the best way to prevent heartworm infection. A simple blood test performed in the veterinarian's office will let you know if your dog is infected with the parasite. If the test is negative your dog will be put on a monthly heartworm preventative. This preventative kills the microfilaria before they have a chance to grow into adults. A positive test means adult worms are present. The infected dog will need to undergo a rigorous treatment to destroy the heartworms before they can cause permanent damage to the heart.